Field of the Invention
The invention relates in general to a tone map selecting device and method, and more particularly to a tone map selecting device and method capable of selecting a tone map according to a bit number per symbol.
Description of the Related Art
In a power line communication (PLC) system, a signal receiver estimates the signal-to-noise ratio (SNR) of received signals in different time intervals and returns the estimated results to a signal transmitter, which is then allowed to accordingly select an appropriate signal carrier modulation scheme. That is, given that a target bit error rate (BER) is satisfied, the signal transmitter determines a signal carrier modulation scheme suitable for a time interval, and such determined result is referred to as a tone map.
In addition respective tone maps of the intervals, a default tone map may be used as a tone map of any interval. The default tone map is usually a tone map of an unusable interval that needs to be re-evaluated. Once a tone map of a certain interval is deemed invalid, the interval becomes the foregoing unusable interval that needs to be re-evaluated. At this point, the signal transmitter uses the unusable interval to transmit data according to the default tone map until the tone map of the unusable interval has been re-evaluated. Thus, the default tone map needs to immediately reflect channel conditions to prevent a high BER of the data transmitted.
There are three common approaches for selecting a tone map in known technologies—using a tone map of quadrature phase-shift keying (QPSK) as a default tone map, using a newly re-evaluated tone map as a default tone map, and always adopting an original default tone map. However, all of the three approaches suffer from drawbacks of not being able to reflect current channel conditions nor consider conditions of the intervals.